[PATCH] regulator: da9062: Replace zero-length array with flexible-array member

[PATCH] regulator: da9062: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertenly introduced[3] to the codebase from now on.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/regulator/da9062-regulator.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-regulator.c
index b064d8a19d4c..c3b6ba9bafdf 100644
--- a/drivers/regulator/da9062-regulator.c
+++ b/drivers/regulator/da9062-regulator.c
@@ -86,7 +86,7 @@ struct da9062_regulators {
 	int					irq_ldo_lim;
 	unsigned				n_regulators;
 	/* Array size to be defined during init. Keep at end. */
-	struct da9062_regulator			regulator[0];
+	struct da9062_regulator			regulator[];
 };
 
 /* BUCK modes */
-- 
2.25.0

RE: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member

[Adam Thomson]

On 11 February 2020 23:46, Gustavo A. R. Silva wrote:

> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertenly introduced[3] to the codebase from now on.
> 
> This issue was found with the help of Coccinelle.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  drivers/regulator/da9062-regulator.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-
> regulator.c
> index b064d8a19d4c..c3b6ba9bafdf 100644
> --- a/drivers/regulator/da9062-regulator.c
> +++ b/drivers/regulator/da9062-regulator.c
> @@ -86,7 +86,7 @@ struct da9062_regulators {
>  	int					irq_ldo_lim;
>  	unsigned				n_regulators;
>  	/* Array size to be defined during init. Keep at end. */
> -	struct da9062_regulator			regulator[0];
> +	struct da9062_regulator			regulator[];

I don't think is the correct change here for this driver. In the probe
'struct_size()' is used to determine the actual size requested from 'malloc()'
when allocating memory for this structure. It's not statically initialised.
Your change will break that code I believe.

>  };
> 
>  /* BUCK modes */
> --
> 2.25.0

Re: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

On 2/12/20 05:12, Adam Thomson wrote:
> On 11 February 2020 23:46, Gustavo A. R. Silva wrote:
> 
>> The current codebase makes use of the zero-length array language
>> extension to the C90 standard, but the preferred mechanism to declare
>> variable-length types such as these ones is a flexible array member[1][2],
>> introduced in C99:
>>
>> struct foo {
>>         int stuff;
>>         struct boo array[];
>> };
>>
>> By making use of the mechanism above, we will get a compiler warning
>> in case the flexible array does not occur last in the structure, which
>> will help us prevent some kind of undefined behavior bugs from being
>> inadvertenly introduced[3] to the codebase from now on.
>>
>> This issue was found with the help of Coccinelle.
>>
>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
>> [2] https://github.com/KSPP/linux/issues/21
>> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>> ---
>>  drivers/regulator/da9062-regulator.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-
>> regulator.c
>> index b064d8a19d4c..c3b6ba9bafdf 100644
>> --- a/drivers/regulator/da9062-regulator.c
>> +++ b/drivers/regulator/da9062-regulator.c
>> @@ -86,7 +86,7 @@ struct da9062_regulators {
>>  	int					irq_ldo_lim;
>>  	unsigned				n_regulators;
>>  	/* Array size to be defined during init. Keep at end. */
>> -	struct da9062_regulator			regulator[0];
>> +	struct da9062_regulator			regulator[];
> 
> I don't think is the correct change here for this driver. In the probe
> 'struct_size()' is used to determine the actual size requested from 'malloc()'
> when allocating memory for this structure. It's not statically initialised.
> Your change will break that code I believe.
> 

Dynamic memory allocations won't be affected by this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Thanks
--
Gustavo

RE: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member

[Adam Thomson]

On 12 February 2020 14:29, Gustavo A. R. Silva wrote:

> On 2/12/20 05:12, Adam Thomson wrote:
> > On 11 February 2020 23:46, Gustavo A. R. Silva wrote:
> >
> >> The current codebase makes use of the zero-length array language
> >> extension to the C90 standard, but the preferred mechanism to declare
> >> variable-length types such as these ones is a flexible array member[1][2],
> >> introduced in C99:
> >>
> >> struct foo {
> >>         int stuff;
> >>         struct boo array[];
> >> };
> >>
> >> By making use of the mechanism above, we will get a compiler warning
> >> in case the flexible array does not occur last in the structure, which
> >> will help us prevent some kind of undefined behavior bugs from being
> >> inadvertenly introduced[3] to the codebase from now on.
> >>
> >> This issue was found with the help of Coccinelle.
> >>
> >> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> >> [2] https://github.com/KSPP/linux/issues/21
> >> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> >>
> >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> >> ---
> >>  drivers/regulator/da9062-regulator.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-
> >> regulator.c
> >> index b064d8a19d4c..c3b6ba9bafdf 100644
> >> --- a/drivers/regulator/da9062-regulator.c
> >> +++ b/drivers/regulator/da9062-regulator.c
> >> @@ -86,7 +86,7 @@ struct da9062_regulators {
> >>  	int					irq_ldo_lim;
> >>  	unsigned				n_regulators;
> >>  	/* Array size to be defined during init. Keep at end. */
> >> -	struct da9062_regulator			regulator[0];
> >> +	struct da9062_regulator			regulator[];
> >
> > I don't think is the correct change here for this driver. In the probe
> > 'struct_size()' is used to determine the actual size requested from 'malloc()'
> > when allocating memory for this structure. It's not statically initialised.
> > Your change will break that code I believe.
> >
> 
> Dynamic memory allocations won't be affected by this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Yeah, ok misinterpreted the descriptions in there. In which case:

Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>

> 
> Thanks
> --
> Gustavo